Systems for press forming glass sheets for use, for example, as automotive windshields, sidelites and/or backlites, may include one or more stations at which glass sheets heated to the softening point of glass are press formed between upper and lower molds into a desired shape (either in the heated ambient or outside the heated ambient), and quenching stations into which the press formed glass sheet is transported for controlled application of a cooling medium (such as air) to the glass sheet to introduce stresses into the sheet adequate for inducing a desired break pattern should the glass break.
In some of these press forming systems, the lower mold is an open center ring which supports the peripheral edge of the glass sheet during press forming. Existing systems also often utilize the same glass sheet support ring to transport the glass sheet to the quench station and support the glass sheet therein during quenching. However, existing rings have proven unsatisfactory in part because the demand for, and development of, more complex shaped automotive lites, and because of decreasing tolerances required for these parts to meet with improved fit and finish standards.
In particular, existing pressing and quenching rings typically employ designs which limit the amount of contact between the supporting surface of the ring and the glass sheet to allow as much of the quenching medium to impinge on as much of the glass sheet surface as possible. For example, rings often employ spaced-apart metal projections which are covered with a screen or wire mesh to limit the ring surface area in contact with the glass sheet. U.S. Pat. No. 3,741,743 discloses a glass sheet shaping frame which utilizes a heavy wire mesh and a fine wire mesh mounted thereon. Another existing design utilizes a wrap of insulating material on the ring to limit the heat transfer between the glass sheet and the relatively cooler support ring which can result in uneven tempering of the edge. U.S. Pat. No. 4,525,196 discloses glass sheet handling devices, including a quench ring, provided with glass sheet engaging surfaces composed of a phenolic resin reinforced with fibers of an aromatic polyamide composition.
Existing designs have proven inadequate in meeting the increasingly high tolerances required of curved automotive lites, since there is significant variation in the surface configuration of the pressing ring due to the imprecise fit, bending and/or fracture of the wire mesh screens and/or cloth on the pressing/quenching ring. Also, it is increasingly difficult to fabricate and install press rings having pressing surfaces matching the complex design contour of the glass within more demanding tolerances. And, even when fabricated within tolerance, the ring may warp slightly (i.e., .+-.3 mm over the perimeter or .+-.6 mm across the major dimension of the part) during installation and/or after extensive use. Thus, a need exists for a method for fabricating press/quench rings having a more accurate pressing surface, and for providing for field tuning of the shape of the ring, when required, to produce parts within design tolerances.